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08-30-2016, 07:49 AM   #1
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Aperture ring not working when mounting older K lens

Hello-I am new here and I have tried mounting my "smc Pentax-M f2" lens onto my K-01. I followed all the instructions. I watched several videos and read several articles on how to do this. The problem I have is that the aperture ring does nothing when I move it to various f-stops. It appears to be stuck open on f2. The aperture ring works fine. I enabled the camera for the aperture ring but when I change f stops and press the green button it does not change the exposure setting at all. All the images come out with very shallow depth of field. I have tried reconfiguring the camera several times but it is always this same issue. Any thoughts? The only thing that was not clear is do I have to reconfigure the menu before the lens is mounted or does this make any difference?

08-30-2016, 08:13 AM   #2
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It is not supposed to move when you turn the ring. Only during shot, or for "green-button" metering. It will be wide-open the rest of the time if mounted and the camera is on. (I think on the K-01 it opens up when you power it up cause it is mirrorless -- every DSLR model it is open if mounted.)

Camera should be in M mode, and TURN OFF auto-iso (this is usually the gotcha -- it is in TAV mode on K-01 if auto-iso is enabled, not true Manual. ISO must be set to fixed number).

See here, if you haven't already:

https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html
08-30-2016, 10:56 AM   #3
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This might be related to a mechanical problem, which unfortunately is sometimes present in older lenses: sticky aperture blades.

The lens' aperture is made from several blades of very thin sheet metal which are surface treated and very slightly oiled so that they can move freely, allowing the aperture to open and close as desired. If that oil gets old, it might lead to the opposite effect, braking or completely hindering the blades' movement.

You can check that for yourself:

Remove the lens from the camera, move the aperture ring to the smallest aperture (largest number, should be 22 with your lens) and look through the lens. Do you see the aperture blades?

If you can't see the aperture blades, they're stuck in the full open position. Your lens needs servicing.

If you can see them, carefully move the aperture lever on the lens' backside. The aperture should open now. When you release the aperture lever, the aperture should close quite fast now.

If the aperture closes noticeably sluggish, then the oil on the aperture blades has become sticky and your lens needs servicing.
08-30-2016, 11:07 AM   #4
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QuoteOriginally posted by vonBaloney Quote
It is not supposed to move when you turn the ring. Only during shot, or for "green-button" metering. It will be wide-open the rest of the time if mounted and the camera is on. (I think on the K-01 it opens up when you power it up cause it is mirrorless -- every DSLR model it is open if mounted.)
Not just every DSLR, but most SLRs too. It is called open-aperture metering. If you turned the aperture ring and the aperture closed before you took the picture, the screen (or viewfinder in other cameras) would become too dark to focus or even see, depending on the aperture. The lens will stop down to your chosen aperture once the exposure is taken.

08-30-2016, 12:25 PM   #5
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QuoteOriginally posted by builttospill Quote
Not just every DSLR, but most SLRs too. It is called open-aperture metering. If you turned the aperture ring and the aperture closed before you took the picture, the screen (or viewfinder in other cameras) would become too dark to focus or even see, depending on the aperture. The lens will stop down to your chosen aperture once the exposure is taken.
Of course, I was just making a distinction between being powered up or not -- if memory serves the K-01 doesn't open the lens up until the power is on unlike all the SLRs.
08-30-2016, 01:06 PM   #6
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QuoteOriginally posted by vonBaloney Quote
Of course, I was just making a distinction between being powered up or not -- if memory serves the K-01 doesn't open the lens up until the power is on unlike all the SLRs.
Interesting that it doesn't until power-up. I should have worded my earlier post more carefully. I was adding to the helpful info you had already given; rereading my post it sounded a little abrasive. Sorry.
08-30-2016, 01:31 PM   #7
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Does the K-01 have any mechanical shutter at all, or just an electronic one? If electronic, then it probably does that to prevent light from hitting the sensor when it is not in use. I have some old webcams that would eventually deteriorate in terms of image quality, I believe because they were always exposed to light without a lens cap.
08-30-2016, 02:19 PM   #8
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QuoteOriginally posted by leekil Quote
Does the K-01 have any mechanical shutter at all, or just an electronic one? If electronic, then it probably does that to prevent light from hitting the sensor when it is not in use. I have some old webcams that would eventually deteriorate in terms of image quality, I believe because they were always exposed to light without a lens cap.
It has a shutter, but of course no optical viewfinder so you can never look through it like an SLR when it is off. (Although unlike the SLRs, on the K-01 the shutter is closed and covering the sensor when the power is off, making it less prone to pick up dust during lens changes -- at least at that moment, you may still be letting some particles into the interior that may migrate to the sensor later.)

Still a little strange about the aperture since it is a K-mount like the rest and obviously they are all designed so the aperture lever is held open mechanically when mounted, power or not. So when removing the mirror mechanism from the design, they removed that part also.

08-30-2016, 08:05 PM   #9
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OK, I have a K-01 and tried it with an M style lens (Takumar 135mm) and the K-01 is a bit quirky with the M style lenses. The K-01 does have a mechanical shutter which stays closed when the camera is off and opens up as soon as the camera is turned on. When you take the shot, the shutter closes, then fires for the shot, then opens again. Realistically, it is always in a Live View mode.

It seems when you stop down the lens to ascertain an f/stop-to-shutter speed exposure setting (more on this in a moment), the viewfinder/monitor automatically compensates for the lack of light, bumping up the image brightness on the display. This makes it very hard to judge the exposure before shooting, so you pretty much have to guess and chimp the shot. The aperture is working as the DoF increases as you stop down, but the effect of exposure on the monitor is neutralized. I was hoping the K-01 would provide changes to the exposure meter, but there is no indication for this in the camera monitor display.

To stop down the lens before the shot, place the camera into M mode. Make certain the Aperture Ring option is set to Enabled, and when you press the +/- button next to the Red button on the top of the camera, the lens will stop down. This will work as a DoF preview nicely, but not work well for exposure settings, as mentioned. Another option, put the camera into Tv mode and let the shutter speed float as needed. This works quite nicely and if you need to over or underexpose an image to get the shot you want, then use that same +/- button to adjust the exposure compensation.

Remember, these older style M lenses were never designed with a mirrorless camera in mind!

---------- Post added 08-30-16 at 11:11 PM ----------

QuoteOriginally posted by vonBaloney Quote
Of course, I was just making a distinction between being powered up or not -- if memory serves the K-01 doesn't open the lens up until the power is on unlike all the SLRs.
Yes, your memory serves you well. The aperture stops down when off, opens up as soon as the K-01 is powered on.

Last edited by BigDave; 08-30-2016 at 08:11 PM.
09-01-2016, 08:20 PM   #10
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Thanks for all the responses. I will play around with it again this week-end.
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